The problem might be trying too hard. When it comes to separating your astral body from the physical, you need to be relaxed. You can either imagine yourself floating above your physical body, or sinking into your bed and getting out of the physical. I prefer the first one though.
Also, fear can cause problems. If you are afraid of what's going to happen when you leave your physical body, don't be. Nothing's impossible in the astral world. There's no need to be scared because you can do anything there. If you see something that looks dangerous, you can either scream or move your hand, it will disappear if you believe that it will.
I would still say "stay relaxed and don't try too hard". When you reach that state, just do one of those visualization tricks, or you can try other methods. Those two are the most effective techniques for myself, however you can search, learn and practice other methods as well. Hope you succeed.
It's pretty normal because those spells do not work. Those are fantasy spells and will never work. A spell cannot change your DNA. It cannot physically change your nature.
The reason is because magick is not made of physical energy. Yes, magick is energy but not the same energy in the physics. So, when something doesn't have a physical basis, it cannot do something physical.
You may or may not believe it or even try more spells to assure yourself. That's fine. You can test them and as you've already seen, get to the final decision of that they don't work but you should not insist. Use your common sense. If a spell would turn someone into a vampire, then why would many knowledgeable people on the site deny its existence?
Many people, however, still insist on the spells working or even some dare enough to share their ignorance by claiming to be one. I can only say, no. They are not vampires or anything similar. Whoever claims to be one is surely proving his/her nonsense.
From what science has proven till now, it is not possible to just turn into a fairy-tale character. Which means if you find a spell that allows you to physically change into a mermaid, werewolf, vampire, etc, it will not work and you shouldn't waste your time on it.
If anyone claims to be any of the above, In the "physical form", do not believe them. You can ask for proof, you will see that they are suddenly busy and have to leave!
To be honest even if they existed, they wouldn't waste their time trying to tell others, they would keep it a secret and enjoy being unique.
There ARE spiritual paths such as the Werewolf path and Vampyrism, but they are totally different from being a role player. As far as I can remember even the werewolf path calls some people "Pseudo Werewolves". Pseudo Werewolves are those who claim that they can physically shape-shift into a wolf. Same goes with Vampyrism, vampire fluffs are not allowed there.
And again, you can not change your DNA with a spell. Do not trust whatever you see there. Most of them don't even know what magick means.